Michael M. Driessen

The distribution and host range of the pandemic disease chytridiomycosis in Australia, spanning surveys from 1956–2007

Chytridiomycosis is the worst disease to affect vertebrate biodiversity on record. In Australia, it is thought to have caused the extinction of four frog species, and it threatens the survival of at least 10 more. We report the current distribution and host range of this invasive disease in Australia, which is essential knowledge for conservation management. We envisage that the data be used in a global and national context for predictive modeling, meta-analyses, and risk assessment. Our continent-wide data set comprises 821 sites in Australia and includes 10 183 records from >80 contributors spanning collection dates from 1956 to 2007. Sick and dead frogs from the field and apparently healthy frogs from museum collections were tested opportunistically for the presence of Batrachochytrium dendrobatidis, the fungal pathogen causing chytridiomycosis, and apparently healthy frogs and tadpoles found during surveys were tested purposively. The diagnostic tests used were histology of skin samples and quantitative PCR of skin swabs. Chytridiomycosis was found in all Australian states and the Australian Capital Territory, but not in the Northern Territory. Currently it appears to be confined to the relatively cool and wet areas of Australia, such as along the Great Dividing Range and adjacent coastal areas in the eastern mainland states of Queensland, New South Wales, and Victoria, eastern and central Tasmania, southern South Australia, and southwestern Western Australia. Batrachochytrium dendrobatidis may have been introduced into Australia via the port of Brisbane around 1978 and spread northward and southward. It did not appear to arrive in Western Australia until 1985. The earliest records from South Australia and Tasmania are from 1995 and 2004, respectively, although archival studies from these states are lacking. We also report negative findings showing that the disease does not currently occur in some areas that appear to be environmentally suitable, including Cape York Peninsula in Queensland and most of the World Heritage Area in western Tasmania. Infection with B. dendrobatidis has been recorded from 63 frog species in Australia to date, all belonging to the Hylidae, Limnodynastidae, and Myobatrachidae, with the exception of one individual of a species from the Microhylidae and the introduced cane toad of the family Bufonidae.

Status and conservation of the rodents of Tasmania

Compared with mainland Australia the diversity of rodents in Tasmania is low. In all, there are five species of native rodent in Tasmania. Three species – the water rat, Hydromys chrysogaster, the long-tailed mouse,Pseudomys higginsi and the swamp rat, Rattus lutreolus – are widely distributed. The broad-toothed rat, Mastacomys fuscus, is restricted to moorlands in western Tasmania, while the New Holland mouse, Pseudomys novaehollandiae, is restricted to coastal heath in north-eastern Tasmania and is listed as Rare under Tasmania’s Threatened Species Protection Act 1995. Only one species, Pseudomys higginsi, is endemic to Tasmania. Rattus lutreolus velutinus and Mastacomys fuscus fuscus are endemic subspecies. In addition to the native rodents, three species of exotic rodents are well established in Tasmania.

The projected distributions of Mastacomys fuscus and Rattus lutreolus in south-eastern Australia under a scenario of climate change: potential for increased competition?

Animal distribution is strongly controlled by climate, especially at higher altitudes where harsher conditions favour fewer vertebrate species. A predicted consequence of climate change is increased pressure on these higher-altitude faunal communities by invasion of lower-altitude species more suited to warmer conditions. The distribution of two such species, the broad-toothed rat (Mastacomys fuscus) and swamp rat (Rattus lutreolus) (with the former generally occurring at higher altitude except in Tasmania), were examined using BIOCLIM. Modelled climate change with a 20% reduction in precipitation and a warming of 2.9°C at latitude 36°S (Snowy Mountains) and 3.4°C at 42°S (central Tasmania) suggests that M. fuscus will retreat to higher altitudes. The core areas of R. lutreolus will also contract, but significantly they will also move so that they overlap current core areas of M. fuscus on the mainland. Barrington Tops is the northernmost known location for M. fuscus and is climatically marginal. The recent invasion of Barrington Tops by R. lutreolus and decline of M. fuscus raises the question as to whether the modelled broader range changes will result in greater competition between the invading R. lutreolus and the cool-climate specialist M. fuscus, resulting in the further loss of the latter.

Distribution and risk factors for spread of amphibian chytrid fungus Batrachochytrium dendrobatidis in the Tasmanian Wilderness World Heritage Area, Australia

Chytridiomycosis is an emerging infectious disease caused by the pathogen Batrachochytrium dendrobatidis (Bd) and is the cause of the decline and extinction of amphibian species throughout the world. We surveyed the distribution of Bd within and around the Tasmanian Wilderness World Heritage Area (TWWHA), a 1.38 million ha area of significant fauna conservation value, which provides the majority of habitat for Tasmanias 3 endemic frog species (Litoria burrowsae, Bryobatrachus nimbus and Crinia tasmaniensis). Bd was detected at only 1 (3%) of the 33 sites surveyed within the TWWHA and at 15 (52%) of the 29 sites surveyed surrounding the TWWHA. The relatively low incidence of the disease within the TWWHA suggests that the majority of the TWWHA is currently free of the pathogen despite the fact that the region provides what appears to be optimal conditions for the persistence of Bd. For all survey sites within and around the TWWHA, the presence of Bd was strongly associated with the presence of gravel roads, forest and < 1000 m altitude--factors that in this study were associated with human-disturbed landscapes around the TWWHA. Conversely, the presence of walking tracks was strongly associated with the absence of Bd, suggesting an association of absence with relatively remote locations. The wide distribution of Bd in areas of Tasmania with high levels of human disturbance and its very limited occurrence in remote wilderness areas suggests that anthropogenic activities may facilitate the dissemination of the pathogen on a landscape scale in Tasmania. Because the majority of the TWWHA is not readily accessible and appears to be largely free of Bd, and because Tasmanian frogs reproduce in ponds rather than streams, it may be feasible to control the spread of the disease in the TWWHA.

Moving with the times: baseline data to gauge future shifts in vegetation and invertebrate altitudinal assemblages due to environmental change

Abstract A long-term monitoring program has been established in Tasmania, Australia, as a Satellite Project for the International Biodiversity Observation Year (IBOY). This program aims to monitor distributional change in vegetation and fauna assemblages along an altitudinal gradient (70–1300 m) in response to climate change and other environmental events. Baseline data collected over a two-year period will be available for comparison with data collected in future decades. The vegetation varies with altitude and fire history. The rate of change in vegetation is not continuous along the altitudinal gradient, but is most rapid above 700 m and below the treeline at 1000–1100 m. Most vascular plant species reach the limit of their distribution within this zone. Despite their preliminary nature, the invertebrate data also display altitudinal and seasonal patterns. The treeline and the 700–1000 m zone again appear to be notable in terms of invertebrate distribution. While the composition of ground-based taxa may be closely related to the floristic composition of the vegetation (or its environmental drivers), the airborne invertebrate fauna appears to be more closely related to structural characteristics such as height and density. Of all taxa, the Coleoptera appear to be the best potential indicators across most altitudes and times. Although the current data provide a wealth of inventory and distributional information over altitude, their greatest potential value lies in long-term comparative information. Future sampling should focus not only on changes at and above the treeline, but also on the zone below this where many species are at their altitudinal limits and may be particularly sensitive to climate change.

Demography and home range of the eastern barred bandicoot (Perameles gunnii) in south-eastern Tasmania

We used live-trapping to study the demography and movement of two populations of the eastern barred bandicoot, Perameles gunnii, in south-eastern Tasmania from 1992 to 1996. Densities were 0.35–2.35 animals ha–1. Sex ratios were male-dominated on Grid I and female-dominated on Grid II. The average body weight for sexual maturity was 700g for males and 680g for females, while the lowest recorded weight for a breeding female was 570g. Perameles gunnii was sexually dimorphic, with males having a greater body weight and pes length than females. Recruitment was 25.4–32.1%, residence 46.7–100.0%, and emigration 16.5–25.5% of the population. Three juveniles were recruited to the Grid I population, 55 to Grid II, with a steady decline in the number of juveniles recruited to Grid II over the four years of the study. Breeding occurred year-round. Mean litter size was 2.53, with 78.2% of all litters having either 2 or 3 young. Mean longevity for male and female P. gunnii was 7.91 and 10.54 months, respectively. Home ranges of males (4.29 ha) were significantly larger than those of females (2.34 ha), although this may represent a significant underestimate due to the small width of our grids (200m) relative to the home-range area. There was only moderate overlap (19.3%) between home ranges of males and females. The overlap between male/male home ranges (4.4%) was significantly less than the overlap between female/female home ranges (15.8%). Perameles gunnii carried both ticks and fleas, with flea infestation being significantly higher on Grid I than on Grid II. Both populations underwent a significant decline over the study period, apparently the result of the unusually dry conditions over the first 3 years of the study. A deterioration in conditions was associated with a steady loss of resident adults, declining recruitment of juveniles and an increase in the male/female sex ratio. The sex ratio of P. gunnii populations may provide a convenient index of habitat quality, with poor or deteriorating conditions apparently associated with a high or increasing numbers of males to females.

Diggings as a Population Index for the Eastern Barred Bandicoot

Quick, efficient techniques for monitoring populations are vital in ecological studies. Transect methods provide one possible means of monitoring local numbers. We investigated the usefulness of the diggings of the eastern barred bandicoot (Perameles gunnii), an endangered, small-medium sized marsupial of southeastern Australia as an index of population size using a modification of the kilometric index. Total diggings and mean transect diggings were correlated with P gunnii numbers on 2 trapping grids in southeastern Tasmania. When grids were combined, mean transect diggings provided a reasonably accurate estimate of animal numbers. We suggest that digging counts provide a quick and efficient method for monitoring changes in local populations of P. gunnii.

Distribution, prevalence and persistence of mucormycosis in Tasmanian platypuses (Ornithorhynchus anatinus)

While the fungal disease mucormycosis has infected Tasmanian platypuses for nearly three decades, its impacts remain largely unknown. This study documents the spatial and temporal distribution of mucormycosis in Tasmanian platypuses as a baseline for assessing its impacts. Over 1800 platypus capture and observation records were collated and mapped, and indicate that between 1982 and 2007 mucormycosis-infected platypuses were present in at least 11, and potentially 22, of Tasmania’s 48 river catchments. During 2008–09, live-trapping surveys were undertaken to determine the spread, prevalence and persistence of the disease. Surveys of 75 rivers and creeks across 18 catchments captured 167 individuals, and an additional 12 platypuses were obtained from the public. Only seven of the 179 sampled animals were ulcerated with clinical signs of mucormycosis. All infected individuals were obtained from catchments with prior histories of disease, where platypuses have persisted despite mucormycosis being present for up to 20 years. Detection probabilities were calculated to estimate the probability that the other surveyed catchments are currently disease free. Detection probabilities were generally high (>0.75) per catchment, indicating that sampling effort was adequate to reliably detect diseased animals at historically reported prevalence (which averaged 0.295 from surveys undertaken between 1994 and 2000). Mean disease prevalence in affected catchments sampled during the present study declined to 0.071. This significant four-fold reduction in prevalence makes disease detection more challenging and increased sample sizes are required to confidently assert that some catchments are currently disease free. Reduced disease prevalence suggests that mucormycosis is exerting less impact on Tasmanian platypuses now than it was in the mid to late 1990s; however, the individual consequences of infection are poorly understood and require further investigation.

The implications of succession after fire for the conservation management of moorland invertebrate assemblages

Fire management in protected areas requires an understanding of the consequences of fire regimes. Invertebrates are a key component of biological communities, but studies of fire impacts on diverse invertebrate assemblages over long timeframes are rare. The responses of ground- and foliage-active invertebrate assemblages to fire in buttongrass moorlands were investigated using a space-for-time design. Assemblages in recently burnt moorlands were distinct from those in older moorlands. Contrary to expectations, ground-active invertebrate abundance, but not taxon richness, was greatest in young regrowth (2–3 years since last fire), owing to large populations of Formicidae, Orthoptera, Collembola and Diptera. Foliage-active invertebrate assemblages followed the expected trend with least numbers of invertebrates and taxa in young regrowth. Very few taxa (n = 9) were absent from young successional stages and none were absent from later successional stages. Invertebrate assemblages in moorlands on low productivity soils took approximately twice as long to return to their pre-fire state than assemblages on moderate productivity soils. The shifts in invertebrate composition were associated with shifts in vegetation composition. Vegetation density was found to be a potentially important predictor of invertebrate compositional variation. Fire in buttongrass moorland appears to have a limited impact on ground-active and foliage-active invertebrate assemblages, suggesting that these components of the invertebrate fauna are resilient to fire (i.e. able to return to the pre-fire state). Given that fire impedes successional processes that convert moorlands into rainforest, and eliminate many of the moorland invertebrate species, conservation management of moorlands should involve the acceptance or imposition of fire.

Shifts in Composition of Monthly Invertebrate Assemblages in Moorland Differed Between Lowland and Montane Locations but not Fire-Ages

ABSTRACT Understanding seasonal changes in invertebrate populations is important for understanding ecosystem processes and for conservation of invertebrate communities. Few studies have investigated variation in seasonal responses of multiorder and multispecies invertebrate assemblages. To determine whether temporal patterns in invertebrate assemblages and taxa vary between locations and vegetation age since burning, patterns of invertebrate occurrence were investigated monthly for 12 mo in cool temperate buttongrass moorlands at two locations (lowland and montane) containing paired plots with different fire history (young and old regrowth). For both locations and fire-ages, invertebrate taxon richness and abundance were generally higher during the warmer months than during the winter months. At the lowland location, foliage dwelling invertebrates were caught in greater numbers during winter than during summer owing to large numbers of Collembola. Each season had a distinct invertebrate assemblage. The invertebrate assemblages did not differ between young and old regrowth. The shifts in composition of monthly invertebrate assemblages between winter and summer differed between locations with assemblages in cooler months more dissimilar from warmer months at the montane location than the lowland location. Most taxa common to both locations had similar patterns of monthly occurrence but some taxa showed markedly different patterns. Mid- to late summer is the optimum time to conduct short-term surveys in buttongrass moorland to maximize species richness and abundance but short-term studies will miss significant components of the invertebrate community.